With respect to a conventional manufacturing method for antireflection films, a method in which desired numbers of low refractive-index layers and high refractive-index layers are formed on a substrate with their thickness being controlled is widely used. However, this method generally requires a vacuum equipment, thereby failing to provide a method with high cost performance. For this reason, various structures without requiring a vacuum equipment or with less number of layers have been proposed.
Among these methods, with respect to a method for using a ultra-low-refractive-index layer in which holes and air voids are introduced therein as the low-refractive-index layer so as to greatly improve the antireflection property, for example, in one proposed method, a fine particle layer with voids being located between the particles is formed on the substrate by using a coating method. This method provides a low-reflectance achieved by continuous changes in the refractive index obtained by the surface shaping effect of fine particles, the low-reflectance being also achieved by bulk (the layer thickness specified by the particle size) refractive-index reduction (average refractive-index reduction) by utilizing the voids between particles (where the refractive-index of voids is 1); thus, it is possible to obtain an antireflection film having high performances by using a simple manufacturing method.
Examples of such a method include a coat film filled most closely with fine particles and a manufacturing method thereof (Japanese Patent Application Laid-Open No. 7-198904), a coat film with fine particles being dispersed and held in one layer by utilizing a binder layer having a thickness smaller than the particle size (Japanese Patent Application Laid-Open No. 5-42211), a coat film having a layer of substrate on which porous fine particles are formed (Japanese Patent Application Laid-Open No. 5-13021), and an antireflection film having a structure in which a binder section of a film formed by ultra-fine particles that are dispersed and held as one layer by a binder is removed by a dry etching process and voids are introduced between particles, and a manufacturing method thereof (Japanese Patent Application Laid-Open No. 7-104103), etc.
Moreover, an antireflection film which is allowed to have similar functions as the above-mentioned particle layers by providing fine irregularities on a coat layer has been proposed. Examples thereof include: an antireflection film in which fine irregularities are formed by etching a layer composed of ultra-fine particles and a binder and a manufacturing method thereof (Japanese Patent No. 2858821), and an antireflection film (Ullrich Steiner, et. al. Science, volume 283, page 520, 1999) made by a method in which fine air voids and holes are formed in a polymer blend thin-film by its micro phase separation and solvent extraction of specific components from the polymer, etc.
The above-mentioned various methods are all based upon simple processes as their concept, and have respective problems. In other words, first, with respect to the various methods for forming one particle layer, the process for forming one particle layer on a substrate is carried out by a coating method that is typically represented by a slide coating method, or a dip coating method. In the coating method typically represented by a slide coating method, it is very difficult to provide a uniform coating operation without allowing particles to aggregate as irregular lumps, while the region having no particles is being reduced to an area that is sufficiently small so as not to impair the visibility, and another problem is that the coating rate is not raised so high.
Here, the dip coating method also has similar problems, and in particular, with respect to the coating speed (the substrate raising speed), this needs to be set to as small as several tens μ msec−1 in order to obtain a uniform particle most-closely filled structure (Nagayama, et al. Langmuir, vol 12, page 1303, 1999; Japanese Patent No. 2905712); therefore, this makes the method very difficult to be put into practical use from the industrial point of view.